[rrd-users] Re: rrdtool resets (sorry)

[BAARDA, Don]

G'day,

> -----Original Message-----
> From:	Christian Pearce [SMTP:pearcec at PacketPushers.com]
> Sent:	Saturday, January 27, 2001 2:57 PM
> To:	Paul Wickman
> Cc:	Christian Pearce; rrd-users at list.ee.ethz.ch
> Subject:	[rrd-users] Re: rrdtool resets (sorry)
> 
> 
> Lookin at the code and following the values during a reset.  How does it
> calculate the interval that had the reset occur during it.  I thought the
> interval would go NAN since the delta should be negative.  But it looks
> like it calculates a value.
> 
	Remember that counters can "zero" because of a wrap, not just a
reset, and RRD has no way to differentiate the two. So RRD treats a negative
delta for a COUNTER as a wrap by default. If it was actually a reset, this
would _normaly_ result in an unlikely value (ie, huge). So the only way RRD
can mark a reset interval as "UNKNOWN" is if the value for that interval
looks unreasonable; ie, too big.

> I take it the DERIVE is the right thing to do and I believe in my mind it
> is correct.  I just would like to be able to explain why it is correct to
> my boss and everyone else that asks.  Any takers?
> 
	I haven't seen all of your earlier posts so I'm not 100% familiar
with your setup, but it sounds like what you actually want is a COUNTER with
a reasonable max. Using DERIVE with min=0.0 will mark not only resets, but
also legitimate counter wraps as "Unknown".

	It always pays to have reasonable min and max values.  

> Christian Pearce
> -PacketPusher
> 
> On Fri, 26 Jan 2001, Paul Wickman wrote:
> 
> > 
> > 
> > Use DERIVE instead of COUNTER.  That, in combination with rrd-min=0 will
> > eliminate the "reset effect".  You will loose the offending sample, but
> in
> > my (and many other people's) case, it's a worthty tradeoff.
> > 
> > 
> 
> 
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